The present invention relates to an improved apparatus and method for plasma processing and, in particular, an improved apparatus and method for plasma etching semiconductor substrates.
In the field of semiconductor processing, vacuum processing chambers are generally used for etching and chemical vapor deposition (CVD) of materials on substrates by supplying an etching or deposition gas to the vacuum chamber and application of an RF field to the gas to energize the gas into a plasma state. Examples of parallel plate, transformer coupled plasma (TCP(trademark)) which is also called inductively coupled plasma (ICP), and electron-cyclotron resonance (ECR) reactors and components thereof are disclosed in commonly owned U.S. Pat. Nos. 4,340,462; 4,948,458; 5,200,232 and 5,820,723. U.S. Pat. No. 4,793,975 also discloses a parallel plate plasma reactor.
During processing of semiconductor substrates, the substrates are typically held in place within the vacuum chamber on substrate holders by mechanical clamps and electrostatic clamps (ESC). Examples of such clamping systems and components thereof can be found in commonly owned U.S. Pat. Nos. 5,262,029 and 5,838,529. An example of a monopolar chuck can be found in U.S. Pat. No. 4,665,463 and examples of bipolar chucks can be found in U.S. Pat. Nos. 4,692,836 and 5,055,964. In order to cool the substrates, cooling gas such as helium can be supplied to the backside of the substrate. Examples of such cooling can be found in U.S. Pat. Nos. 5,160,152; 5,238,499; and 5,350,479.
Substrate supports can include consumable (sacrificial) edge rings around the substrate for purposes of confining plasma to the area above the wafer and/or protect the ESC from erosion by the plasma. For instance, an edge ring arrangement is described in commonly owned U.S. Pat. Nos. 5,805,408; 5,998,932; 6,013,984; and 6,039,836. Other examples of edge ring arrangements can be found in U.S. Pat. Nos. 5,494,523; 5,986,874; 6,022,809; 6,096,161; and 6,117,349.
In plasma processing arrangements wherein a sacrificial ring surrounds a wafer, it would be desirable to improve the thermal contact between the ring and an underlying portion of the substrate support. By improving thermal coupling, improved temperature control of the ring could be realized and the clearances required between the ring and the wafer could be reduced. It would also be desirable if the RF impedance path from the baseplate to the plasma in the area above the wafer could be more closely matched to the RF impedance path from the baseplate to the plasma in the area of the edge ring in order to improve plasma uniformity near the edge of the wafer.
The present invention provides an edge ring clamping assembly adapted to surround a substrate support in a plasma reaction chamber. The edge ring clamping assembly includes a member having an annular support surface and an electrostatic edge ring chuck on the support surface. According to one embodiment, the edge ring chuck comprises an outer portion of a ceramic body mounted on the substrate support and the ceramic body includes an electrostatic wafer chuck located radially inward of the edge ring chuck. According to another embodiment, an axially extending groove is located in the annular support surface and the groove is adapted to receive a mating projection of an edge ring clamped on the edge ring chuck. Optionally, at least one gas passage extends through the member and the edge ring chuck such that a heat transfer gas can be supplied to an exposed surface of the edge ring chuck. The edge ring chuck can comprise a bipolar chuck and/or an edge ring of electrically conductive material can be clamped to the member by the edge ring chuck.
The present invention also provides a plasma reaction chamber comprising a substrate support on which a wafer to be processed can be mounted and an electrostatic edge ring chuck on which an edge ring can be supported during processing. In one embodiment, the substrate support comprises a temperature controlled electrode adapted to maintain the edge ring below a threshold temperature by heat conduction from the edge ring to the substrate support. In another embodiment, the edge ring includes a recess on an inside edge of an upper surface thereof and the recess is adapted to fit beneath a wafer mounted on the substrate support with a clearance gap between the edge ring and the wafer of no more than about 0.003 inch. The substrate support can comprise an RF driven electrode and/or the plasma reaction chamber can comprise a parallel plate reactor such as an etch chamber having an upper electrode facing the baseplate.
The present invention also provides a method of treating a semiconductor substrate such as a wafer in a plasma chamber wherein the plasma chamber comprises a substrate support, an electrostatic wafer chuck on an upper surface of the substrate support and an electrostatic edge ring chuck on which an edge ring can be supported. In a preferred embodiment, the method comprises the steps of electrostatically clamping a wafer to the wafer chuck, electrostatically clamping an edge ring to the edge ring chuck, supplying a process gas to the interior of the plasma chamber, energizing the process gas into a plasma state, and processing the wafer with the plasma. During the process, a heat transfer gas can be supplied to an interface between the edge ring and the edge ring clamp to maintain the temperature of the edge ring below a threshold temperature.